Field of the Invention
The present invention relates to a refrigerant-circulating system, and a refrigerant compressor and a refrigeration cycle such as a freezer or an air-conditioner, employing the refrigerant compressor. More particularly, it relates to a refrigerator oil composition which is suitable to alternative refrigerants a containing no chlorine from the aspect of the protection of the ozone layer and excellent in the compatibility with the refrigerant, the low temperature flowability, thermochemical stability, wear resistance, anti-seizing property and electrical insulation property, and a refrigerant compressor containing said composition, provided with machinery parts, electrical insulating materials or the like excellent in the chemical stability, wear resistance, anti-seizing property and electrical insulation property, and a refrigeration cycle employing this refrigerant compressor.
In recent years, from the viewpoint of protection of ozone layer, it has been regulated to limit the use of freon type refrigerants such as CFC or HCFC containing chlorine which have been employed for refrigerators, freezers, dehumidifiers and air-conditioners.
Under such circumstances, as an alternative refrigerant, hydrofluorocarbon (HFC) and hydrocarbon (HC) which contain no chlorine and have a low reactivity with ozone and a short term for decomposition in air, have been studied and practiced.
However, such alternative refrigerants containing no chlorine in the molecule all have a high polarity and show poor compatibility with conventional refrigerator oils such as a mineral oil or an alkylbenzene oil which have been used for refrigeration cycles of refrigerants containing chlorine Accordingly, developments of new refrigerator oils have been made.
FIG. 15 shows a refrigeration cycle used for conventional alternative refrigerants described in JP-A-8-240351. FIGS. 16(a) and (b) are cross-sectional views of a general refrigerant compressor used for refrigeration cycles suitable for conventional alternative refrigerants. FIG. 16(a) is a vertical cross-sectional view and FIG. 16(b) is a cross-sectional view seen from the upper face of a cylinder.
Here, 101 is a refrigerant compressor, 102 is a closed container, 103 is an evaporator, 104 is a condenser, and 105 is an expansion mechanism such as an expansion valve or a capillary tube. A hydrated fluorocarbon (HFC) containing no chlorine is encapsulated in the circuit to form the refrigeration cycle.
In the closed container 102 of the refrigerant compressor 101, an electrically driving element 106 and a compressing element 107 are contained and a refrigerator oil 180 is stored at the bottom. Further, the electrically driving element 106 comprises a stator 109 and a rotor 110, and the stator 109 comprises a wiring portion 111 and a core portion 112, and electric power is supplied from a hermetically sealed terminal 113 to the electrically driving element 106 through a lead wire. The compressing element 107 is composed of a main shaft 114 connected to the rotor 110, a rolling piston 115 engaged with an eccentric part of the main shaft 114, a cylinder 116 which defines a compression chamber, a main bearing 117 and a sub bearing 118 which close the side faces of the cylinder 116 and at the same time support the main shaft 114, a vane 119 which is slidingly in contact with the outer periphery of the rolling piston 115 and partitions off the compression chamber into a high pressure part and a low pressure part, and a vane spring 120.
The refrigerant compressor 101 is connected to the refrigeration cycle by means of an intake tube 121 and a discharge tube 122.
Now, the operation of conventional refrigeration cycle will be described.
When the compressor is operated, the rotation force of the electrically driving element 106 is transferred to the compressing element 106 by means of the main shaft 114 connected to the rotor 110, whereby the rolling piston 115 engaged with the eccentric portion of the main shaft 114 is eccentrically rotated in the cylinder 116. The vane 119 which partitions off the cylinder 116 into a high pressure part and a low pressure part, is reciprocally moved while the terminal end of the vane 119 is being in contact with the outer periphery of the rolling piston 115 by the back pressure and the spring force of a vane spring 120.
The refrigerant is introduced into the cylinder 116 through the intake tube 112, and compressed by the eccentric rotation of the rolling piston 115 and discharged to the inside of the closed container 102 from the cylinder 116, and then used to cool the electrically driving element 106 and introduced to the external refrigeration cycle through the discharge tube 122.
The overheated refrigerant gas of a high pressure and a high temperature discharged from the refrigerant compressor 101, undergoes heat exchange with the external air by means of the condenser 104 to remove the latent heat, whereby it becomes a refrigerant liquid of a high pressure and a high temperature. Then, the refrigerant becomes a saturated refrigerant liquid of a low pressure by the pressure reduction by means of the expansion mechanism 105, and further undergoes heat exchange with the external air by means of the evaporator 103 to let the latent heat absorbed, whereby it becomes a refrigerant gas.
Here, the refrigerator oil 180 stored at the bottom of the closed container 102 of the refrigerant compressor 101, is supplied from the lower end of the main shaft 114, and used for lubrication of respective sliding parts of the compressing element 107, and then major part thereof is returned to the bottom of the closed container 102, but a part thereof is discharged to the external portion of the refrigerant compressor 101 through the discharge tube 122 along with the refrigerant gas and circulated in the refrigeration cycle, and returned to the refrigerant compressor 101 through the intake tube 121 again.
Accordingly, the refrigerator oil used for the refrigeration cycle is firstly demanded to have a high compatibility with the refrigerant within a wide temperature range of from a low temperature to a high temperature and be excellent in the low temperature flowability, since it is circulated along with the refrigerant.
Further, with conventional refrigerants containing chlorine such as chlorofluorocarbon (CFC) or hydrochlorofluorocarbon (HCFC), the chlorine molecules function as an extreme-pressure additive on the surface of sliding parts and show extremely good lubricating properties. Whereas, with alternative refrigerants containing no chlorine which do not destroy the ozone layer, such extreme-pressure effect of the refrigerants themselves can not be expected, whereby refrigerator oils used for such alternative refrigerants are required to have excellent wear resistance, anti-seizing property, thermal stability and chemical stability in order to lubricate the sliding parts at a high temperature and a high pressure.
Further, since the refrigerator oil is used for the electrically driving element 106 in the closed container 102, whereby it is demanded to have excellent insulating properties as well.
JP-A-1-259093 discloses as a refrigerator oil suitable to a halogenated fluorocarbon (HFC) refrigerant, ones containing propylene glycol monoether (PAG) represented by the following formula (2), as a base oil. ##STR1##
wherein R is an alkyl group.
Further, JP-A-1-259094 discloses a diether type compound formed by etherifying the terminal end of propylene glycol. However, it is generally known that the PAG oil is poor in the electrical insulating properties, moisture absorptivity, wear resistance and anti-seizing property, and can not be practically used for a closed type refrigerant compressor.
JP-A-8-240351 discloses a refrigerator oil suitable for a hydrogenated fluorocarbon (HFC) refrigerant, containing as a base oil, an ester oil of aliphatic acid having at least two ester bonds (--O--CO--) in the molecule, as indicated by the following formulas, for example, a hindered type ester or a complex type ester of a branched structure having a polyhydric alcohol and a C.sub.6-8 aliphatic acid. EQU (R.sub.1 --CH.sub.2).sub.2 --C--(CH.sub.2 COOR.sub.2).sub.2 (3) EQU R.sub.1 --CH.sub.2 --C--(CH.sub.2 --COOR.sub.2).sub.3 (4) EQU C(CH.sub.2 --CHOOR.sub.2).sub.4 (5) EQU (R.sub.2 --OOCH.sub.2 C).sub.3 --C--CH.sub.2 --O--CH.sub.2 --(CH.sub.2 --COOR.sub.2).sub.3 (6)
where R.sub.1 is H or a C.sub.1-3 alkyl group, and R.sub.2 is a C.sub.5-12 alkyl group and may be a mixture of various types of alkyl groups having different carbon numbers.
Further, JP-A-8-151590 discloses a refrigerator oil composition comprising a polyol ester as a base oil, and based on the base oil, from 7.0 to 15.0 wt % of a phosphate and from 0.2 to 3.0 wt % of 1,2-epoxyalkane and/or vinylcyclohexene dioxide.
These ester oils are now most widely studied as refrigerator oils suitable for alternative refrigerants by virtue of their excellent electrical insulation properties and moisture absorptivity.
Further, studies are being made on a polyvinyl ether oil of the following formula. (Reference can be made to the following document.) ##STR2##
wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are alkyl groups having different carbon numbers, and each of n and m is an integer of at least 1.
("Performance of a new ether oil for HCFCs alternative refrigerants on practical use" by Minoru Takagi, "The International Symposium On HCFC Alternative Refrigerants '96, page 141, Proceedings Dec. 5-6, 1996, International Conference Center Kobe, The Japan Refrigeration and Air Conditioning Industry Association")
As described above, studies have heretofore been made on oxygen-containing hydrocarbon type synthetic oils such as ester type synthetic oils and polyvinyl ether type synthetic oils.
With respect to the ester type synthetic oils, studies have been most widely made by virtue of their superior properties to the polyether type synthetic oils, for example, excellent lubrication property, excellent electrical insulation property and low moisture absorptivity.
However, the ester oil is a synthetic oil formed by dehydration condensation reaction of an aliphatic acid and an alcohol and this reaction is reversible, whereby it tends to undergo hydrolysis in the presence of water. Further, it is known that when an acid is liberated by hydrolysis, corrosion and wearing will be caused. EQU RCOOR'+H.sub.2 O.fwdarw.RCOOH+R'OH (8) EQU FeO+2RCOOH.fwdarw.Fe(OCOR).sub.2 +H.sub.2 O (9)
Since the reaction with metals is accelerated if a fresh face is formed by wearing, hydrolysis tends to be accelerated in the rotary type compressor in which the inside of the closed container 102 is maintained at a high temperature and a high pressure and which has sliding parts where fluid lubrication is hardly performed such as the terminal end of the vane 119 and the periphery of the rolling piston 115.
The wearing by hydrolysis or the deterioration of the refrigerator oil tends to cause problems that sludges are deposited in the expansion mechanism 105 such as capillary tubes or expansion valves in the refrigeration cycle and clogging of the expansion mechanism 105 is thereby caused, leading to failure in cooling or ordinary operation.
To cope with such problems, studies have been made on the base oil structure having a branched chain taking the hydrolysis into consideration and the additives such as epoxy in order to capture and neutralize the free aliphatic acid after hydrolysis, and on the types or amounts of extreme-pressure additives in order to reduce the wearing which accelerates the hydrolysis. However, the hydrolysis is necessarily unavoidable since the ester structure is possessed in the molecule.
Further, in the case of air-conditioner, since an exterior device and an interior device are connected at the time of installation work, water content may be incorporated into the refrigeration cycle in the installation work, and it is impossible to control strictly the water content only in the factory. Accordingly, by using the ester oil as the refrigerator oil, clogging of the expansion mechanism 105 and failure in cooling may be caused.
On the other hand, with respect to the ether oil, although the hydrolysis which is the drawback of the ester oil is not caused, the ether bond is likely to cause problems that deterioration by oxidation is likely caused, the lubricity is inferior, and wearing or scuffing are likely caused at the terminal end of the vane 119, the outer periphery of the rolling piston 115 or the like on which severe sliding conditions are demanded.
Further, there is a drawback that the ether oil is poor in the insulation property necessary for the refrigerator oil for the refrigerant compressor.
It is an object of the present invention to provide a highly reliable refrigerant-circulating system employing a new refrigerator oil which solves the problems of the refrigerator oils used for the refrigerant-circulating systems for conventionally studied alternative refrigerants, by analysis and researches on practical use conditions in the production steps of the practical manufacturing sites, the installation work and the market of the refrigerant-circulating systems and the refrigerant compressors, in order to solve the above-mentioned problems.
It is another object of the present invention to define an optimum viscosity range for the viscosity grade of the refrigerator oil, which decisively affects the reliability and energy efficiency of the refrigerant-circulating system and compressor, under the operational conditions of the refrigerant-circulating system and the refrigerant compressor in general purpose operations such as freezing, refrigeration, air-conditioning and dehumidification.
It is an object of the present invention to provide improvements by use of additives for a new refrigerator oil and methods for improving insulation properties and the constitution of the refrigerant-circulating system, by which highly reliable refrigerant-circulating systems can be provided even in the case where a high pressure type rotary type compressor is used in a refrigerant compressor used for severe environment for the use of the refrigerator oil, or in the case where long existent pipelines containing a large amount of contamination is used.
It is an object of the present invention to provide a highly reliable method useful for the case where a retrofitting operation wherein a refrigerant containing chlorine used for an existent refrigerant-circulating system is changed to a refrigerant containing no chlorine, is conducted.
It is another object of the present invention to provide a highly reliable refrigerant compressor having a high performance, which contains a refrigerator oil having an excellent compatibility with a refrigerant containing no chlorine and excellent lubricity, chemical stability and the like.
It is an object of the present invention to provide a refrigerant compressor provided with machinery parts such as a bearing, a spring and a seal material which are excellent in e.g. chemical stability, wear resistance and anti-seizing property, suitable for such combination of the refrigerant and the refrigerator oil.
It is an object of the present invention to provide a refrigerant compressor provided with a hermetically sealed terminal, a wiring for a stator and a core portion of a stator which are excellent in e.g. chemical stability and electrical insulation property, suitable for such combination of the refrigerant and the refrigerator oil.
It is an object of the present invention to provide a highly reliable refrigeration cycle employing the refrigerant containing no chlorine and the above-mentioned refrigerant compressor.